(1) Field of the Invention
The present invention relates to a coating composition which is applicable to outdoor building structures or outdoor structures for the purpose of decoration or protection, and which is capable of forming a film having excellent properties in crack resistance, flexibility, stain resistance, water resistance, alkali resistance, acid resistance, and the like.
(2) Description of the Prior Art
A highly weather resistant outdoor coating composition as a coating composition applicable to outdoor structures and the like has been developed in the art. Particularly, acrylic silicone resin based coating composition and fluorocarbon resin based coating composition have been considered suitable as outdoor coating composition because of improvement in film resistance to deterioration due to sun light, rain and the like. However, the above coating compositions have such drawbacks that during outdoor exposure, pollutants adhere onto the surface of a coating film to show poor film appearance under the influence of dust, sand dust, iron powder, acid rain as recent problem, etc. in atmosphere.
As a method of preventing adhesion of dust in atmosphere, a method of adding various antistatic agents such as Electrostripper TS-2B (marketed by Kao Corporation, trade name, surfactant based one) and Colcote R (marketed by Colcote Co., Ltd., trade name, alkylsilicate based one), which are capable of reducing the surface resistivity value of the coated film and preventing static adhesion of dust, etc., to a coating composition, or of coating the antistatic agents onto the surface of the film for treating, has been disclosed. However, the above method is unsuitable for outdoor use, because the added antistatic agents show poor water resistance, resulting in making it difficult to maintain the above static adhesion preventing effect.
Japanese Patent Application Laid-Open No. 306328/94 discloses a highly acid rain resistant organic coating composition prepared by adding a condensation product between an, alkylsilicate oligomer and a silane coupling agent such as a hydrolyzate of an epoxy-functional silane to a coating composition.
However, the above organic coating composition has such drawbacks that the above condensation product consists of a mixture of an alkylsilicate oligomer, silane coupling agent oligomer and block condensation product of both oligomers, and consequently the epoxy group of the hydrolyzate of an epoxy-functional silane is not uniformly introduced in the condensation product, but the remaining alkylsilicate oligomer is eluted by water, resulting in that the coated film shows poor water resistance, particularly poor alkali resistance, as well as such drawbacks that the coated film may cause cracks on forming a film and further shows unsatisfactory flexibility.